CA1131765A - Television camera - Google Patents
Television cameraInfo
- Publication number
- CA1131765A CA1131765A CA315,186A CA315186A CA1131765A CA 1131765 A CA1131765 A CA 1131765A CA 315186 A CA315186 A CA 315186A CA 1131765 A CA1131765 A CA 1131765A
- Authority
- CA
- Canada
- Prior art keywords
- control
- pick
- picture signal
- tube
- stage
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
- H04N23/40—Circuit details for pick-up tubes
- H04N23/41—Beam current control
-
- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
- H04N23/00—Cameras or camera modules comprising electronic image sensors; Control thereof
- H04N23/10—Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from different wavelengths
- H04N23/13—Cameras or camera modules comprising electronic image sensors; Control thereof for generating image signals from different wavelengths with multiple sensors
Landscapes
- Engineering & Computer Science (AREA)
- Multimedia (AREA)
- Signal Processing (AREA)
- Processing Of Color Television Signals (AREA)
- Picture Signal Circuits (AREA)
- Details Of Television Scanning (AREA)
Abstract
PHN. 8969.
18-4-1978.
ABSTRACT :
A television camera comprising a control and setting stage for the beam current control of an electron beam in a pick-up tube. Via an substantially video frequency picture signal amplifier suitable for supplying the picture signal over substantially the entire amplitude range over which the pick-up tube generates the picture signal, via a coupling capacitor the picture signal generated by the pick-up tube is superimposed as a control voltage on the setting voltage for the control electrode of the pick-up tube. A stable beam current control without oscillations is the result.
18-4-1978.
ABSTRACT :
A television camera comprising a control and setting stage for the beam current control of an electron beam in a pick-up tube. Via an substantially video frequency picture signal amplifier suitable for supplying the picture signal over substantially the entire amplitude range over which the pick-up tube generates the picture signal, via a coupling capacitor the picture signal generated by the pick-up tube is superimposed as a control voltage on the setting voltage for the control electrode of the pick-up tube. A stable beam current control without oscillations is the result.
Description
~3~65 The invention relates to a television camera comprising at least one pick-up tube and a con-trol circuit for the intensity control of an electron beam present in the pick-up tube, the electron beam being generated by an electron gun comprising at least a cathode and a control electrode, an output, carrying a picture signal, of the pick-up tube being connected for beam current intensity control to a control input of the control circuit, an output of which, carrying a control signal, being connected to the control electr-ode in the pick-up tube, the control circuit comprising a setting stage for an adjustment of the beam current intensity and a control stage for an automatic control thereof.
Such a camera is described as prior art camera in German Auslegeschrift 24 24 402 Hitachi filed May 20, 1974. It is described that the picture signal generated by the pick-up tube is subjected to the fol-lowing processes in the control circuit: the picture signal is first amplified, thereafter a black level in the picture signal is clamped on a reference level by means o~ a clamping circuit and then that signal portion which exceeds a nominal peak-white value is separated from the picture signal and, via a low-pass filter in which the smoothed signal is
Such a camera is described as prior art camera in German Auslegeschrift 24 24 402 Hitachi filed May 20, 1974. It is described that the picture signal generated by the pick-up tube is subjected to the fol-lowing processes in the control circuit: the picture signal is first amplified, thereafter a black level in the picture signal is clamped on a reference level by means o~ a clamping circuit and then that signal portion which exceeds a nominal peak-white value is separated from the picture signal and, via a low-pass filter in which the smoothed signal is
- 2 -;~`
`\
1~3176S
PHN. 8969.
18-4 1978.
superimposed on a d.c. voltage for adjustment, applied to the control electrode of the electron gun in the pick-up tube.
It is described that a drawback of the prior art camera is that oscillations can and will in practice frequently occur owing to the feedback. As regards the cause or possible several causes, respectively, of the oscillations it is remarked that an exact indica-- tion cannot be given. ~inally the described camera is said to be highly instable and unsuitable for practice.
' It is an object of the inventi on to provide a camera, comprising a control circuit for the beam cur-rent control in which no oscilla-tions caused by this ' 'control occur~ A practically properly operating camera according to the invention comprises a control circuit which is c'haracterized in that the control stage comprises, provided between the control input of the circuit and the ; output of the control stage, a substantially video fre-,I quency picture signal amplifier suitable for supplying 2~ the picture signal over substantially the entlre ampli-tude range over which the pick-up tube generates the picture signal, -the outpu-t of the control stage 'being connected -Lhrough a coupling capacitor to,the output of the setting stage and at the salne time to the control e:lectrode.
A telev;sion can!era suitable for colour 113176~
PH~. 89Gg.
1~-4-1978.
tel.evision and provided to this end with at ].east two pick-up tubes is-characterized in that a single control stage and at least two setting stages are provided, each of these setting stages being connected by means of a setting stage output to the control elec-trode of the electron. gun of one of the pick-up tubes~ these control ~ electrodes of the pick-up tubes each being comlected via a coupling capacitor to the output of the control stage, the control circuit comprising a-t least two control inputs connected to the picture signal outputs of the pick-up tubes, which control inputs are connected to said video frequen.cy picture signal amplifier via a circuit for passing the picture signa:L having the instantaneous highest value.
A practically properly operating television camera is characterized in that the video frequency pic-ture signa] amplifier comprises an amplitude limiter.
A likewise practically properly operating i television caInera is characterized in -that tlIe substant-ially video frequency picture signal amplifier comprises a bandwidth limiter resu:Lting in a bandwidth limitation to the orcler o~ magnitude of 1.5 mHz.
To prevent darnage to the electron gUIl a ~ camera is furtherrIlore charactcrized in that the connect-Z5 ion of sai.d couplirlg capacitor to the control elec1rode of the elec-tron gurI o~ one of the pick-up tubes is con-113~76~
PMN. 8g6~.
. 18-4-1~78.
nected via the anode-cathode path o~ a diode to a supply terminal for the catllode of the electron gun of the pick-up tube.
The invention will be further explained by way of non-limitative example with reference to the accompanying ~igure.
Reference numerals 1s 2 and 3 in the Figure denote three pick-up tubes which are part of 2 colour television camera. The pick-up tubes 1, 2 and 3, which are implemented in the same manner, are shown schematically, having onl.y those components which are important for describing the invention so that, for example, deflection and focussing means provided at the -- pick-up tubes 1, 2 and 3 have been omit~ted. ~or the pick~
up tube 1 the following components are denoted in greater detail as examp].e for tlle tubes 1, 2 and 3: a cathode 4, a cont;rol electrode 5, an accelerating electrode 6 and a target pl.ate 7. The target plate 7 consi.sts of a . transparent 7 electrically conducting signal electrode on w]~icll a semi-condllctor layer is provided which is scanned by an e]ectron beam 8 produced by an electron gun (4, 57 6). ~or the electron beam 8, it is desirable to keep the beam currenL intensity as low as possible as with t.he smal.l.er beam d:i.ameter detai.ls in the potential image Oï
the scene on the semiconductor layer are processed with a greater resolut;ion than with a wider beam. On the o-ther PHN. 8969~
18-4 1978.
hand the beam eurrent intensity must be so high that in-the short period in whieh the electron beam 8 is in a given position, sufficient electrie eharge is supplied . for eompensating for the eharge whieh was aeeumulated under the influenee of ineident light deriving from the seene, whieh eharge is present on the semiconductor ' ~ layer of the target plate 7. Because of thls sueh vol-tages are supplied in a manner still to be deseribed - to ~he eathode 4 and the eontrol eleetrode 5 that there is an appropriate adjustMent of the beam current :inten-sity for processing seene portions of a normal light intensity while the current intensity is insL;antaneouslv eonsiderably increased by the processing of scene por~
' tions having an exeessive light intensity.
The connectioll of the target plate 7 of the pick-u.p tube 1 is conn.ected. _ a a resistor 9 to ground and furthermore to the input of a si.gnal ampJ.ifier 10. The sarne applies to the pick-up tubes 2 ancl 3 tlle ' target pla.te connection of which is connected via a resistor 11 and 12, respeetively, to ground and to the input of an arnpli.I'i.er 13 ancL 1~1S respeetively. The output of th.e arnpliI'ier 10, 13 anc1 1LI, respecti..ve:L.y, is connect-ed t;o an 01ltpU.t terminal 1~, 16 a.nd 17, respecti.vely, ancl to a eontrol input 1~, lg and 20, :respectively, of 2~ a eontrol c:ircuit to be describecl still furtl!er~ At the output of the anlplir:ie-r 10~ 13 and 14~ respectively, tllere ~131~65 PH~. 8969.
18-4-1978.
is an amplified picture si.gnal Sl, S2 and S3, respect-ively, which, inverted, is generated by the pick-up tube 1, 2 and 3, respectively, across the resistors 9, 11 and 12, respectively, and which gives a picture of the scene display. The ~igure shows the picture signal S1 by way of example for the picture s:ignals S1, S2 and S3, as a. function of time. Reference b denotes a black level and w a peak-~rhite value, it being possible in the case shown in the drawing that b - 0~, w = ~iV. The signal S1 also shows a signal peak which by far axceeds tlhe peak-white v~lue w and which is associated with a local excessive illumlnation caused by a bright light-reflect~
ing or luminous scene detail. The signal. Sl shows t~iro positions ~rhe:re the picture signal is at the black level b, these positions correspondi.ng to the, for television, conventional :Line blanking times.
The picture signals S1, S2 and S3, derived - from the output terminals 155 16 and 17 can be subjected prior to the ultimate display to further sLgna.L proces-sings 7 such as gamma correcti.on, aper-tu:re correction, matrixing, additional amplification etc.. ~Tia t;he control inpu-ts 18, 19 and 20 the picture signa]s S19 S2 and S3 occur at the anodes of three respective diodes 21, 22 a.nd 23, ~h.ose cathodes are in~erc.onMected and connected to a resistor 2LI. The otller connecti.oJl of -I.he resis-tor.24 is con.nected to the emitter of a pnp-t;rarislstor.-25, wJlose PHN. 8969.
18-4-1978.
base'is connected to ground vi.a the cathode-anode path of two series-arranged diodes 26 and 27. The diodas 21, 22, 23, 26 and 27, the resistor 24 and the transistor 25 constitute together a circuit ,~21 - 27) for passing the picture signal of the instantaneous highest value of the three pi.c-ture signals S1, S2 and S3 applied thereto.
~or simpli.city it is assumed that the signal S1 has for the entire duration, shown in the dra~ing, the highest - installtaneolls value of th.e three picture signais S1, S2 and S3 and consequently deterrnines the col.lect'or current of t'he transistor 25.
The base of the diode 26, wllich base is con-nected to 1,h.e cathode of transistor 25, is connected to the cathode of' a zener diode 28 wh.ose anode carries a voltage of`~ for ex~mple~ -45V via a connection, to be described further i.n the course of khis doscription, to a supp:Ly -terminal carrying a negative voltage. The collector of the transistor 25 is connected to tlle anode connecting point of -45V vi.a a resistor 29,.via a capa--c:itor 30, vi.a a series arrangement of a diode 31 and a zen.er diode 32 and _a the base-emitter path of an npn-transistor 33 in series with a resistor 34. The co]lec-tor of -the transistor 33 :is con-llected to groundO The junctivn of the em:Ltter of` the transistor 33 and the resistor 34 is connected -i,o an olltpUt 35 of a control stage ('i8~35) thus I`orlrledy which sllpplies a con-trol signal SC shown 113~7~S
PHN. 8969.
1&-4-1978.
in t-he drawing.
The control stage (18-35) comprises sub-stantially video f`requency picture signal amplifier (24-34) for supplying the picture signal S1, S2 or S3~
5 applied thereto, across substantially the whole ampli-tude range across which the piCk-llp tube 1, 2 or 3 ge-nerates the picture signal S1, S2 or S3 . This is illus-trated by means of the control signal SC which, as as~
sumed, i.s derived f`rom the signal S1, at which control signal SC the black level b= 45V and the peak-white value w are plotted and, in addition, a limiting level h is stated. For the operation of the amplifier (24-34) it holds that in the presence of the black level b= o~r at the i3~put 1~, takell by way of e~ample, the transistor 25 is cut-off` as its base has two diode threshold vol-tages (26 and 27) helow the ground. potenti~l and the emitter is lo-wer f`or th.e same amount owing to a d:iode threshold voltage (21) and the base-emitter threshold.
voltage of the tran.sistor 25. Tlhe transistor 33 is like-wise cut-oI`f by the same voltage at the base and the e1nitter, so that the black level b=-45V occurs in the signal SC at the outpu-t 35 via tlle resistor 34 The occurrence in the signal S1 o~ the peali-whi.i;e va].ue w= --1V is f`oulld at an en.Larged scale in tLe signal SC~
! 2~ w]lere;3l~ for e~.ample5 a resi.strlnce ratio of the resis-torS 24 and 29 of one to ten, that is to say a tenfold ~ g _ 1~31765 PHN. 896~.
18-4-1978.
gain, results in a peak-white value w_ -35V in -the signal SC. A voltage U of, for exampl.e, 20V, which is also the maximum voltage which can be present across the series arran.gement o.~ the diode 31 and the zener diode 32, which, together, form an amplitude limiter (31,32) is indicated a-t the signa:l. SC. Tllis implies that the very high signal peaks in the sig:~als S1, S2 or S3, whi.cll can~
for example, be as high as fifteen times and more the peak-white value, are ]imited in the e~amp:Le given to twice the peak-w11ite value w of the signal SC, with w}lich th.e limlting value h=-25~r is associa-ted.
In practice it furthermole appears advan-tageous to uti]ize the picture signal S1, S2 or S3 not with the ~ull bandwidth. in the order o~ magnitude of 5 MHz f`o:r de:riving the control sig11al S~ but to perrorm a bandwid1h l:Lmitat:ion to in the order o:L ma~11itude of 1.5 ~1IIz. T11e amplifier (24 31l) is provided for this purpose wi th a bandwid-t11 limi.tel (29-30)o For ~the c.ontrol purpo;es control outpuS 35 of control sl;age (18-35) i.s conn.ected via a coupling capaciLor 3G, 37 and 38, respectively, to the control elect:rode 5 ol` -t11e pick-up tube 1, 2 or 3~ The control electrode 5 of 1he pi.ck-up tube I is connected for setting purposes to t;l1e set-ti11g oul;p1lt 39 o~ an adjust:ilg ~slage (3~ 2) constit1lted hy fl potentiometer 40 disposed betwee31 the anode col~necting poi:nt o:L the 7.ener diode 28 - 10 ~
PHN. 8969.
and a terminnal having a voltage of -150V, a diode 41, connected -to the potentiometer tap and, at the cathode, to the setting output 39 and via a resi.stor 42 to the terminal having the voltage -150V. Likewise the con.trol electrode 5 of the pick-up tube 2 and 3, respectively, is con3~1ected to a setting output 4-3 and 47, respectively, of a setting stage (43-46) and (~1-7-50), respectively, formed by a potentiometer ~4 and L~8, respectively;
a diode 45 and 49, respectively, and a resistor 46 an.d 50, respectively.
The cathodes 1l of -the pick-llp tubes 1, 2 and 3 are interconnected and, vi.a a change~over stage 51, they are connectable to the anode connecti.ng point of the zener diode 28 having the voltage ~II-5V or to ground. l:ile charlge-over stage 51 i.s operat:ive for the liDe and ~ield blanking for which purpose .Lt is suppliecl with a blaL~ing signal which is s}1.own in the drEt~ringas line b].anking sig:nal SB. In the blankin.g periods the cathode 4~ which then carries the gro~nd lotential sup-plies no electrorl bean1. ¦
The setting outputs 39, 43 and /17 carry the respect;.ve setti.ng voltages ~rl, V~ alld V3.
The se-t-ti.ng voltages V1; V2 ~nd V3 are adjustetl by me.lnC~ of 1he pote]li;iome1;ers l~o, 44 and 48 i:n d.epe3lclent.~y on. t1he para~ne-ters and the~ use~ of th.e pick-up -t~lbcs 1, 2 or 3. 1~lat is requ:iced is -tlla-t during t:he .
~l131765 PHN. 8969.
18-4-1978.
recordi.ng of a scene in which the picture signa.l contains the nominal values'only, the pick-up tubes operate satis-faetorily. It l~olds, for example, that in a colour tele-vision eamera a 2/3" pick-up tube used for generating the greel1, red and blue colour signal respectively ear-ries a beam current of 300 nA, 150 llA and 100 nA respect-ively. The control signal SC is superimposed on the set-ting voltages Vl, V2 and V3 via the coupling capaeitors 36, 37 and 38. The varyi-ng video information in the sig-nal SC resultts in a variation of the voltage on the COJ1 trol e.leetrodes 4$ for whieh it applies that small vol-tage variations of a few volts hardl~r affect the beam eurrent, as is apparent from the current-voLtage eharact-eristics fo3- 'the beam current.aI1d th0 control e]ectrc>cle voltage, specif`:ied in data harldhoo]csO Larger vo;Ltage transients, for exampLe above 10V, inf:luerlce the beam current to a more than propor-tional extent. In practice a stable beam current eontrol appears to oceur with.out unwanted oseil:Lations at a limi-tation of the voltage transient to U = 20V from bl.aclc level b =~l-5V.
The conn.ec-ting point o:~ the control elec-trode 5 of` the pic1~~up -tu'be 1 t:o the eoupling capacito~ 3b and the settill.g ou-tput 39 of the sett-Ln~g stage (39-42) is conl1ected vi-l the arlode~cathode path of a diode 52 -l:o the corlneeti3-g pOil1t carryiJIg a vo.l.tage of -45V and bei.ng eom1eeted to -the cat.hode 4. This was done to obvi.at.e tlle ~ 1 ~ --113~76S
PHN. 8969~
'18_4-1978-possibility that -the control el.ectrode voltage becomes less negative than the cathode voltage, which may, for example, happen if the setting voltage ~i is adjusted less negative than -65V an.d the voltage transient in the control slgnal amounts to U = 20V. I~or the same purpose, that is to say to prevent dama.ge to the electron gun (4,5,6), diodes 53 and 51; are disposed at the set-ting outputs 43 and 47.
It should be noted that tlle cGntrol circuit (18-54) th.us formed for the beam current control9 in es-sence the entire video information being utilized (control signa] SC) by means of the amplifier (2~l-34), operates satisfactorily in practice ~it]l011t disturbing oscilla-A tions, whilst, by way of illustration, some ~ralues Or ~ 5~) the componellts used in the control clrcuit ~ ~ are gi~en: ;
Resistor 24 .1k~
Resistor 29 10k!.
Capacitor 30 10p~`
Resistor 34 10k.
Coupling capaci.tors 36, 37 and 38 IOOnF
Pote~tiometers 40, ~!4 a~ 8 lOOk.
Resistors 42, 46 and 50 1~IS~
`\
1~3176S
PHN. 8969.
18-4 1978.
superimposed on a d.c. voltage for adjustment, applied to the control electrode of the electron gun in the pick-up tube.
It is described that a drawback of the prior art camera is that oscillations can and will in practice frequently occur owing to the feedback. As regards the cause or possible several causes, respectively, of the oscillations it is remarked that an exact indica-- tion cannot be given. ~inally the described camera is said to be highly instable and unsuitable for practice.
' It is an object of the inventi on to provide a camera, comprising a control circuit for the beam cur-rent control in which no oscilla-tions caused by this ' 'control occur~ A practically properly operating camera according to the invention comprises a control circuit which is c'haracterized in that the control stage comprises, provided between the control input of the circuit and the ; output of the control stage, a substantially video fre-,I quency picture signal amplifier suitable for supplying 2~ the picture signal over substantially the entlre ampli-tude range over which the pick-up tube generates the picture signal, -the outpu-t of the control stage 'being connected -Lhrough a coupling capacitor to,the output of the setting stage and at the salne time to the control e:lectrode.
A telev;sion can!era suitable for colour 113176~
PH~. 89Gg.
1~-4-1978.
tel.evision and provided to this end with at ].east two pick-up tubes is-characterized in that a single control stage and at least two setting stages are provided, each of these setting stages being connected by means of a setting stage output to the control elec-trode of the electron. gun of one of the pick-up tubes~ these control ~ electrodes of the pick-up tubes each being comlected via a coupling capacitor to the output of the control stage, the control circuit comprising a-t least two control inputs connected to the picture signal outputs of the pick-up tubes, which control inputs are connected to said video frequen.cy picture signal amplifier via a circuit for passing the picture signa:L having the instantaneous highest value.
A practically properly operating television camera is characterized in that the video frequency pic-ture signa] amplifier comprises an amplitude limiter.
A likewise practically properly operating i television caInera is characterized in -that tlIe substant-ially video frequency picture signal amplifier comprises a bandwidth limiter resu:Lting in a bandwidth limitation to the orcler o~ magnitude of 1.5 mHz.
To prevent darnage to the electron gUIl a ~ camera is furtherrIlore charactcrized in that the connect-Z5 ion of sai.d couplirlg capacitor to the control elec1rode of the elec-tron gurI o~ one of the pick-up tubes is con-113~76~
PMN. 8g6~.
. 18-4-1~78.
nected via the anode-cathode path o~ a diode to a supply terminal for the catllode of the electron gun of the pick-up tube.
The invention will be further explained by way of non-limitative example with reference to the accompanying ~igure.
Reference numerals 1s 2 and 3 in the Figure denote three pick-up tubes which are part of 2 colour television camera. The pick-up tubes 1, 2 and 3, which are implemented in the same manner, are shown schematically, having onl.y those components which are important for describing the invention so that, for example, deflection and focussing means provided at the -- pick-up tubes 1, 2 and 3 have been omit~ted. ~or the pick~
up tube 1 the following components are denoted in greater detail as examp].e for tlle tubes 1, 2 and 3: a cathode 4, a cont;rol electrode 5, an accelerating electrode 6 and a target pl.ate 7. The target plate 7 consi.sts of a . transparent 7 electrically conducting signal electrode on w]~icll a semi-condllctor layer is provided which is scanned by an e]ectron beam 8 produced by an electron gun (4, 57 6). ~or the electron beam 8, it is desirable to keep the beam currenL intensity as low as possible as with t.he smal.l.er beam d:i.ameter detai.ls in the potential image Oï
the scene on the semiconductor layer are processed with a greater resolut;ion than with a wider beam. On the o-ther PHN. 8969~
18-4 1978.
hand the beam eurrent intensity must be so high that in-the short period in whieh the electron beam 8 is in a given position, sufficient electrie eharge is supplied . for eompensating for the eharge whieh was aeeumulated under the influenee of ineident light deriving from the seene, whieh eharge is present on the semiconductor ' ~ layer of the target plate 7. Because of thls sueh vol-tages are supplied in a manner still to be deseribed - to ~he eathode 4 and the eontrol eleetrode 5 that there is an appropriate adjustMent of the beam current :inten-sity for processing seene portions of a normal light intensity while the current intensity is insL;antaneouslv eonsiderably increased by the processing of scene por~
' tions having an exeessive light intensity.
The connectioll of the target plate 7 of the pick-u.p tube 1 is conn.ected. _ a a resistor 9 to ground and furthermore to the input of a si.gnal ampJ.ifier 10. The sarne applies to the pick-up tubes 2 ancl 3 tlle ' target pla.te connection of which is connected via a resistor 11 and 12, respeetively, to ground and to the input of an arnpli.I'i.er 13 ancL 1~1S respeetively. The output of th.e arnpliI'ier 10, 13 anc1 1LI, respecti..ve:L.y, is connect-ed t;o an 01ltpU.t terminal 1~, 16 a.nd 17, respecti.vely, ancl to a eontrol input 1~, lg and 20, :respectively, of 2~ a eontrol c:ircuit to be describecl still furtl!er~ At the output of the anlplir:ie-r 10~ 13 and 14~ respectively, tllere ~131~65 PH~. 8969.
18-4-1978.
is an amplified picture si.gnal Sl, S2 and S3, respect-ively, which, inverted, is generated by the pick-up tube 1, 2 and 3, respectively, across the resistors 9, 11 and 12, respectively, and which gives a picture of the scene display. The ~igure shows the picture signal S1 by way of example for the picture s:ignals S1, S2 and S3, as a. function of time. Reference b denotes a black level and w a peak-~rhite value, it being possible in the case shown in the drawing that b - 0~, w = ~iV. The signal S1 also shows a signal peak which by far axceeds tlhe peak-white v~lue w and which is associated with a local excessive illumlnation caused by a bright light-reflect~
ing or luminous scene detail. The signal. Sl shows t~iro positions ~rhe:re the picture signal is at the black level b, these positions correspondi.ng to the, for television, conventional :Line blanking times.
The picture signals S1, S2 and S3, derived - from the output terminals 155 16 and 17 can be subjected prior to the ultimate display to further sLgna.L proces-sings 7 such as gamma correcti.on, aper-tu:re correction, matrixing, additional amplification etc.. ~Tia t;he control inpu-ts 18, 19 and 20 the picture signa]s S19 S2 and S3 occur at the anodes of three respective diodes 21, 22 a.nd 23, ~h.ose cathodes are in~erc.onMected and connected to a resistor 2LI. The otller connecti.oJl of -I.he resis-tor.24 is con.nected to the emitter of a pnp-t;rarislstor.-25, wJlose PHN. 8969.
18-4-1978.
base'is connected to ground vi.a the cathode-anode path of two series-arranged diodes 26 and 27. The diodas 21, 22, 23, 26 and 27, the resistor 24 and the transistor 25 constitute together a circuit ,~21 - 27) for passing the picture signal of the instantaneous highest value of the three pi.c-ture signals S1, S2 and S3 applied thereto.
~or simpli.city it is assumed that the signal S1 has for the entire duration, shown in the dra~ing, the highest - installtaneolls value of th.e three picture signais S1, S2 and S3 and consequently deterrnines the col.lect'or current of t'he transistor 25.
The base of the diode 26, wllich base is con-nected to 1,h.e cathode of transistor 25, is connected to the cathode of' a zener diode 28 wh.ose anode carries a voltage of`~ for ex~mple~ -45V via a connection, to be described further i.n the course of khis doscription, to a supp:Ly -terminal carrying a negative voltage. The collector of the transistor 25 is connected to tlle anode connecting point of -45V vi.a a resistor 29,.via a capa--c:itor 30, vi.a a series arrangement of a diode 31 and a zen.er diode 32 and _a the base-emitter path of an npn-transistor 33 in series with a resistor 34. The co]lec-tor of -the transistor 33 :is con-llected to groundO The junctivn of the em:Ltter of` the transistor 33 and the resistor 34 is connected -i,o an olltpUt 35 of a control stage ('i8~35) thus I`orlrledy which sllpplies a con-trol signal SC shown 113~7~S
PHN. 8969.
1&-4-1978.
in t-he drawing.
The control stage (18-35) comprises sub-stantially video f`requency picture signal amplifier (24-34) for supplying the picture signal S1, S2 or S3~
5 applied thereto, across substantially the whole ampli-tude range across which the piCk-llp tube 1, 2 or 3 ge-nerates the picture signal S1, S2 or S3 . This is illus-trated by means of the control signal SC which, as as~
sumed, i.s derived f`rom the signal S1, at which control signal SC the black level b= 45V and the peak-white value w are plotted and, in addition, a limiting level h is stated. For the operation of the amplifier (24-34) it holds that in the presence of the black level b= o~r at the i3~put 1~, takell by way of e~ample, the transistor 25 is cut-off` as its base has two diode threshold vol-tages (26 and 27) helow the ground. potenti~l and the emitter is lo-wer f`or th.e same amount owing to a d:iode threshold voltage (21) and the base-emitter threshold.
voltage of the tran.sistor 25. Tlhe transistor 33 is like-wise cut-oI`f by the same voltage at the base and the e1nitter, so that the black level b=-45V occurs in the signal SC at the outpu-t 35 via tlle resistor 34 The occurrence in the signal S1 o~ the peali-whi.i;e va].ue w= --1V is f`oulld at an en.Larged scale in tLe signal SC~
! 2~ w]lere;3l~ for e~.ample5 a resi.strlnce ratio of the resis-torS 24 and 29 of one to ten, that is to say a tenfold ~ g _ 1~31765 PHN. 896~.
18-4-1978.
gain, results in a peak-white value w_ -35V in -the signal SC. A voltage U of, for exampl.e, 20V, which is also the maximum voltage which can be present across the series arran.gement o.~ the diode 31 and the zener diode 32, which, together, form an amplitude limiter (31,32) is indicated a-t the signa:l. SC. Tllis implies that the very high signal peaks in the sig:~als S1, S2 or S3, whi.cll can~
for example, be as high as fifteen times and more the peak-white value, are ]imited in the e~amp:Le given to twice the peak-w11ite value w of the signal SC, with w}lich th.e limlting value h=-25~r is associa-ted.
In practice it furthermole appears advan-tageous to uti]ize the picture signal S1, S2 or S3 not with the ~ull bandwidth. in the order o~ magnitude of 5 MHz f`o:r de:riving the control sig11al S~ but to perrorm a bandwid1h l:Lmitat:ion to in the order o:L ma~11itude of 1.5 ~1IIz. T11e amplifier (24 31l) is provided for this purpose wi th a bandwid-t11 limi.tel (29-30)o For ~the c.ontrol purpo;es control outpuS 35 of control sl;age (18-35) i.s conn.ected via a coupling capaciLor 3G, 37 and 38, respectively, to the control elect:rode 5 ol` -t11e pick-up tube 1, 2 or 3~ The control electrode 5 of 1he pi.ck-up tube I is connected for setting purposes to t;l1e set-ti11g oul;p1lt 39 o~ an adjust:ilg ~slage (3~ 2) constit1lted hy fl potentiometer 40 disposed betwee31 the anode col~necting poi:nt o:L the 7.ener diode 28 - 10 ~
PHN. 8969.
and a terminnal having a voltage of -150V, a diode 41, connected -to the potentiometer tap and, at the cathode, to the setting output 39 and via a resi.stor 42 to the terminal having the voltage -150V. Likewise the con.trol electrode 5 of the pick-up tube 2 and 3, respectively, is con3~1ected to a setting output 4-3 and 47, respectively, of a setting stage (43-46) and (~1-7-50), respectively, formed by a potentiometer ~4 and L~8, respectively;
a diode 45 and 49, respectively, and a resistor 46 an.d 50, respectively.
The cathodes 1l of -the pick-llp tubes 1, 2 and 3 are interconnected and, vi.a a change~over stage 51, they are connectable to the anode connecti.ng point of the zener diode 28 having the voltage ~II-5V or to ground. l:ile charlge-over stage 51 i.s operat:ive for the liDe and ~ield blanking for which purpose .Lt is suppliecl with a blaL~ing signal which is s}1.own in the drEt~ringas line b].anking sig:nal SB. In the blankin.g periods the cathode 4~ which then carries the gro~nd lotential sup-plies no electrorl bean1. ¦
The setting outputs 39, 43 and /17 carry the respect;.ve setti.ng voltages ~rl, V~ alld V3.
The se-t-ti.ng voltages V1; V2 ~nd V3 are adjustetl by me.lnC~ of 1he pote]li;iome1;ers l~o, 44 and 48 i:n d.epe3lclent.~y on. t1he para~ne-ters and the~ use~ of th.e pick-up -t~lbcs 1, 2 or 3. 1~lat is requ:iced is -tlla-t during t:he .
~l131765 PHN. 8969.
18-4-1978.
recordi.ng of a scene in which the picture signa.l contains the nominal values'only, the pick-up tubes operate satis-faetorily. It l~olds, for example, that in a colour tele-vision eamera a 2/3" pick-up tube used for generating the greel1, red and blue colour signal respectively ear-ries a beam current of 300 nA, 150 llA and 100 nA respect-ively. The control signal SC is superimposed on the set-ting voltages Vl, V2 and V3 via the coupling capaeitors 36, 37 and 38. The varyi-ng video information in the sig-nal SC resultts in a variation of the voltage on the COJ1 trol e.leetrodes 4$ for whieh it applies that small vol-tage variations of a few volts hardl~r affect the beam eurrent, as is apparent from the current-voLtage eharact-eristics fo3- 'the beam current.aI1d th0 control e]ectrc>cle voltage, specif`:ied in data harldhoo]csO Larger vo;Ltage transients, for exampLe above 10V, inf:luerlce the beam current to a more than propor-tional extent. In practice a stable beam current eontrol appears to oceur with.out unwanted oseil:Lations at a limi-tation of the voltage transient to U = 20V from bl.aclc level b =~l-5V.
The conn.ec-ting point o:~ the control elec-trode 5 of` the pic1~~up -tu'be 1 t:o the eoupling capacito~ 3b and the settill.g ou-tput 39 of the sett-Ln~g stage (39-42) is conl1ected vi-l the arlode~cathode path of a diode 52 -l:o the corlneeti3-g pOil1t carryiJIg a vo.l.tage of -45V and bei.ng eom1eeted to -the cat.hode 4. This was done to obvi.at.e tlle ~ 1 ~ --113~76S
PHN. 8969~
'18_4-1978-possibility that -the control el.ectrode voltage becomes less negative than the cathode voltage, which may, for example, happen if the setting voltage ~i is adjusted less negative than -65V an.d the voltage transient in the control slgnal amounts to U = 20V. I~or the same purpose, that is to say to prevent dama.ge to the electron gun (4,5,6), diodes 53 and 51; are disposed at the set-ting outputs 43 and 47.
It should be noted that tlle cGntrol circuit (18-54) th.us formed for the beam current control9 in es-sence the entire video information being utilized (control signa] SC) by means of the amplifier (2~l-34), operates satisfactorily in practice ~it]l011t disturbing oscilla-A tions, whilst, by way of illustration, some ~ralues Or ~ 5~) the componellts used in the control clrcuit ~ ~ are gi~en: ;
Resistor 24 .1k~
Resistor 29 10k!.
Capacitor 30 10p~`
Resistor 34 10k.
Coupling capaci.tors 36, 37 and 38 IOOnF
Pote~tiometers 40, ~!4 a~ 8 lOOk.
Resistors 42, 46 and 50 1~IS~
Claims (5)
18-4-1978.
THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS
1. A television camera comprising at least one pick-up tube and a control circuit for the inten-sity control of an electron beam present in the pick-up tube, the electron beam being generated by an electron gun comprising at least a cathode and a control electrode, an output, carrying a picture signal, of the pick-up tube being connected for beam current intensity control to a control input of the control circuit, an output of which, carrying a control signal, being connected to the control electrode in the pick-up tube, the control circuit comprising a setting stage for an adjustment of the beam current intensity and a control stage for an auto-matic control thereof, characterized in that the control stage comprises, provided between the control input of the circuit and the output of the control stage, a sub-stantially video frequency picture signal amplifier suit-able for supplying the picture signal over substantially the entire amplitude range over which the pick-up tube generates the picture signal, the output of the control stage being connected through a coupling capacitor to the output of the setting stage and at the same time to the control electrode.
2. A television camera as claimed in claim 1, suitable for colour television and comprising to that end at least two pick-up tubes, characterized in that a single control stage and at least two setting stages are provided, each of these setting stages being con-nected by means of a setting stage output to the control electrode of the electron gun of one of the pick-up tubes, these control electrodes of the pick-up tubes each being connected via a coupling capacitor to the output of the control stage, the control circuit com-prising at least two control inputs connected to the picture signal outputs of the pick-up tubes, which con-trol inputs are connected to said video frequency pic-ture signal amplifier via a circuit for passing the picture signal having the instantaneous highest value.
3. A television camera as claimed in claim 1, characterized in that the video frequency picture sig-nal amplifier comprises an amplitude limiter.
4. A television camera as claimed in claim 1, 2 or 3, characterized in that the substantially video frequency picture signal amplifier comprises a bandwidth limiter resulting in a bandwidth limitation to in the order of magnitude of 1.5 mHz.
5. A television camera as claimed in claim 1, 2 or 3, characterized in that the connection of said coupling capacitor to the control electrode of the elec-tron gun of one of the pick-up tubes is connected via the anode-cathode path of a diode to a supply terminal for the cathode of the electron gun of the pick-up tube.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| NL7713571A NL7713571A (en) | 1977-12-08 | 1977-12-08 | TELEVISION ROOM. |
| NL7713571 | 1977-12-08 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1131765A true CA1131765A (en) | 1982-09-14 |
Family
ID=19829707
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA315,186A Expired CA1131765A (en) | 1977-12-08 | 1978-10-31 | Television camera |
Country Status (10)
| Country | Link |
|---|---|
| US (1) | US4365271A (en) |
| JP (1) | JPS5487111A (en) |
| AU (1) | AU522628B2 (en) |
| CA (1) | CA1131765A (en) |
| DE (1) | DE2852901C2 (en) |
| FR (1) | FR2411521A1 (en) |
| GB (1) | GB2010053A (en) |
| IT (1) | IT1109635B (en) |
| NL (1) | NL7713571A (en) |
| SE (1) | SE7812474L (en) |
Families Citing this family (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| NL8005920A (en) * | 1980-10-29 | 1982-05-17 | Philips Nv | TELEVISION CAMERA EQUIPPED WITH A CONTROL CIRCUIT FOR THE ELECTRON Beam Current Strength In At Least A RECEPTION TUBE. |
| JPS58142684A (en) * | 1982-02-19 | 1983-08-24 | Hitachi Denshi Ltd | Automatic controlling method and controlling circuit for beam current |
| NL8204022A (en) * | 1982-10-19 | 1984-05-16 | Philips Nv | METHOD FOR ADJUSTING THE CURRENT STRENGTH OF AN ELECTRON BEAM IN A RECEPTION TUBE AND SUITABLE TELEVISION CHAMBER SYSTEM. |
| JPS59100687A (en) * | 1982-11-30 | 1984-06-09 | Victor Co Of Japan Ltd | Color television image pickup device |
| US4598235A (en) * | 1984-03-27 | 1986-07-01 | Ampex Corporation | Method and apparatus for eliminating lag in photoelectric tubes |
| NL8502970A (en) * | 1985-10-30 | 1987-05-18 | Optische Ind De Oude Delft Nv | METHOD FOR PROCESSING IMAGE INFORMATION WITH A WIDE DYNAMIC RANGE WITH A TELEVISION TUBE AND APPARATUS FOR USING THE METHOD |
Family Cites Families (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB974441A (en) * | 1962-06-20 | 1964-11-04 | Marconi Instruments Ltd | Improvements in or relating to television cameras and the like |
| DE2424402C3 (en) * | 1973-05-21 | 1978-08-24 | Hitachi Electronics Ltd. | Method and arrangement for controlling the strength of the electron beam in a vidicon-type image pick-up tube |
| JPS508418A (en) * | 1973-05-21 | 1975-01-28 | ||
| US4151552A (en) * | 1976-05-21 | 1979-04-24 | Hitachi, Ltd. | Automatic beam control circuit responsive to ambient light level having utility in color television camera |
| US4190865A (en) * | 1976-12-13 | 1980-02-26 | Rca Corporation | Video image tube highlight suppression circuit |
-
1977
- 1977-12-08 NL NL7713571A patent/NL7713571A/en not_active Application Discontinuation
-
1978
- 1978-10-31 CA CA315,186A patent/CA1131765A/en not_active Expired
- 1978-12-04 AU AU42182/78A patent/AU522628B2/en not_active Expired
- 1978-12-05 SE SE7812474A patent/SE7812474L/en unknown
- 1978-12-05 IT IT69787/78A patent/IT1109635B/en active
- 1978-12-05 GB GB7847227A patent/GB2010053A/en not_active Withdrawn
- 1978-12-06 FR FR7834367A patent/FR2411521A1/en active Granted
- 1978-12-06 JP JP15014478A patent/JPS5487111A/en active Pending
- 1978-12-07 DE DE2852901A patent/DE2852901C2/en not_active Expired
-
1980
- 1980-09-26 US US06/191,099 patent/US4365271A/en not_active Expired - Lifetime
Also Published As
| Publication number | Publication date |
|---|---|
| DE2852901A1 (en) | 1979-06-13 |
| IT1109635B (en) | 1985-12-23 |
| GB2010053B (en) | |
| IT7869787A0 (en) | 1978-12-05 |
| SE7812474L (en) | 1979-06-09 |
| GB2010053A (en) | 1979-06-20 |
| AU4218278A (en) | 1979-06-14 |
| FR2411521A1 (en) | 1979-07-06 |
| JPS5487111A (en) | 1979-07-11 |
| DE2852901C2 (en) | 1986-05-07 |
| NL7713571A (en) | 1979-06-12 |
| AU522628B2 (en) | 1982-06-17 |
| FR2411521B1 (en) | 1983-05-27 |
| US4365271A (en) | 1982-12-21 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKEX | Expiry |